Electromagnetic device



Jan. 19, 1960 J. F. DRIES ELECTROMAGNETIC DEVICE Filed June 7. 1957INVENTOR. Jerome [fir/e5 ATTORNEY 2,922,088 ELECTROMAGNETIC DEVICEJerome F. Dries, Hales Corners, Wis., ass'iguor to Cutler- Hammer, Inc.,Milwaukee, Wis., a corporation of Delaware Application June 7, 1957,Serial No. 664,377 4 Claims. (Cl. 317-165) This invention relates toelectromagnetic devices and particularly to electromagnetic deviceswhich may be employed as an actuator for a control means.

Devices of this type generallyhave a low value of pull in the armatureopen position and a very steep rise in pull just prior to armaturesealed position. A low value of pull in the open armature position isundesirable from a standpoint of low voltage pickup, and a high sealedpull is undesirable for a quick release from sealed These objects areattained by an electromagnetic device which includes a magnet framehaving a core, an energizing coil mounted on the core, a convex surfaceon the 'frame spaced from the core and an armature mounted on-the framefor rolling movement on the convex surface toward the core when the coilis energized.- Biasing means are provided which acts on the armature tomove the armature away from the core when the coil is deenergized. Theconvex surface is related to the core and armature so that contactbetween the armature and convex surface moves nearer the core and awayfrom the biasing means acting on the armature as the armature movestoward the core. The length of the moment arm with which the magneticforce acts on the, armature decreases and the length of the moment armwith which the biasing means acts on the armature increases as thearmature moves toward the core, thereby reducing the ratio of energyavailable to move the armature at or near sealed position to thatavailable to move the armature at open or unsealed position for anelectromagnetic device of given capacit The rolling contact between thearmature and frame provides a closed magnetic path between the twoparts. An increased pull results.

Means including a pair of non-magnetic links pivotally connected betweenthe frame and armature are provided for supporting the armature on theframe and to allow the armature to roll freely on the convex surfacetoward and away from the core. There is little or no load carried by thelinks thereby minimizing friction between the moving parts.

Other objects and advantages will be pointed out in, or be apparent fromthe specification and claims, as will obvious modifications of the oneembodiment shown in the drawings, in which:

Fig. 1 is a view in side elevation of an electromagnet embodying thepresent invention showing the armature in sealed position;

United States Patent Fig. 2 is a top plan view of the electromagnetshown in Fig. l;

Fig. 3 is a rear elevation view of the electromagnet shown in Fig. 1;

Fig. 4 is a view similar to Fig. 1 but with the links removed and thearmature in a position intermediate that between open and sealedpositions; and

Fig. 5 is a view similar to Fig. 4 but with the armature in unsealed orcompletely open position.

Referring now to the drawings in detail, the electromagnet includes aU-shaped magnet frame 10 preferably of magnetic ingot iron having a baseportion 12 and upstanding legs 14. A cylindrical core 16 preferably ofmagnetic ingot iron with windings or coil 18 is mounted on base 12between legs 14 by a screw 20 extending through a countersunk opening inbase 12 and threaded into the lower end of the core.

An armature 22 of a suitable magnetic material such as Armco metal ismounted for rolling movement toward and away from core, 16 on convexsurfaces 24 formed on the upper edges of arms 14 of the :frame. Thearmature is supported in position on the convex surfaces by a pin 36fastened by silver soldering or other suitable means to the rear edge ofthe armature and extending beyond the sides thereof. Pin 26 is pivotallyconnected to the frame by links 28 of non-magnetic material and pins 30fixedly secured in openings in the upper portions of legs 14 andextending outwardly therefrom. Links 28 are mounted between pin 26 andpins 30 by openings at either end of the links through which the ends ofthe pins extend. Cotter keys 32 are fitted in the ends of the pins tohold the links in assembled position.

The load of the moving armature is carried by the convex surfaces on theframe so there is little or no load carried by the links therebyeliminating much of the friction normally present in devices having anarmature pivoted in a fixed bearing. Links 28 are made from non-magneticmaterial to eliminate magnetic attraction between the links and the pinsand frame to thereby further reduce friction between the moving parts.

The curvature of convex surfaces 24 is such as to eliminate or reduce toa negligible factor any sliding between the armature and frame as thearmature rolls on the convex surfaces under the guiding influence ofpivotally mounted links 28. The curvature may be constructed by wellknown principles used in the design of gears. In the embodiment shown inthe drawings, the constructed curvature approaches very closely the arcof a circle so for facilitating manufacture of the frame the curve ismade as an arc of a circle havinga radius R.

The armature is biased for movement away from core 16 by coil spring 34connected between pin 26 (at cut-out portion 35 inv armature 22) and lug36 on horizontal extension 38 of the base portion 12 of the frame. Aninverted L-shaped stop member 40 rigidly mounted on frame 10 by off-setbracket 42 fastened to legs 14, limits the movement of armature 22 awayfrom core 16 (Fig. 5) under the bias of spring 34.

Fig. 5 shows the electromagnet in the open or unsealed position witharmature 22 engaged by the stop 40. In this position the armaturecontacts convex surface 24 (for purposes of this explanation referenceis made to only one convex surface on one leg of the frame) at point'(axis) P. In the open or deenergized position the spring 34 acting onthe armature produces a moment about point P equal to the forcecomponent F times the distance y. This moment is sufficient to lift thearmature from a horizontal position to that shown in Fig. 5. Uponenergization of the coil, a magnetic force is produced by the coil whichacts on the armature. The component F of such force times the distance xless to the rollingmovementof the armature on such surface.- Theelectromagnet exerts a pull on the armature represented by the,component F jtimes distance x less the component F times the distance y,(although the springcomponent F increases slightly as the armature movestowards the core it is considered constant for purposes of thisexplanation. Component F is greater than component F because thearmature is closer to the core. Howeven'the distance x is less than thedistance and the distance 5 is greater than the distance 3/. Therefore,.the increased force acting on the armature is compensated either whollyor partially by the decreased moment arm x; andthe increased moment army Fig. 1 shows the armature-inclosed or sealed position with the point:of contact moved. up to point (axis) B In this position the-force F actson the armature at a distance x from the point P The work or energyavailable to movethe armature in this position is equal to F times xless F times y Here again the force F v isgreater than forces F and F(Fig. 4 or 5), but the moment arm x has been further reduced and themoment arm y has been further increased to reduce or neutralize theeffect of the increased magnetic force (F exerted on the armature as itmoves toward the core. I

From the above description it is clear that as the armaturemoves fromopen to closed position the distaricefrom the axis of rolling contactand the force acting on the'armature is gradually reduced and thedistance between the-spring force and the axis of rolling contact iscorrespondingly increased. This reduced moment arm of the magnetic forceand increased moment arm of the spring forcetends to level out the steeprise in energy or work available to move the armature as it moves towardthe coil. Thus, the pull or energy available to move the armature fromopen position is increased over that of conventional constructionsproviding improved operation from the standpoint of low voltage pickup.Similarly, the relatively low value of pull at the sealed positionreduces the elfect of residual magnetism and increases the effectiveforce of the return spring to provide a quickreleaseof the armature fromthesealed position Y 1 r arrangement also provides the desirable featureof eliminating the air gap at the pivoted joint between the armature andframe generally present in conventional'constructions. The rollingarmature is in con tinuouscontact with the frame and thereby maintainsaclosed magneticpath for the magnetic lines of force to thereby increasethe magneticpull between the core and armature. V

Although but one embodiment ofthe present invention has been illustratedand described, it will be apparent to those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the spirit of the invention or from the scope of the appendedclaims.

I claim: 7 V

1. In an electromagnetic device, a: magnet frame having a core, anenergizing coil mounted on said core, a

convex surface on said'frame' spaced from said core, anarmature mountedon said frame for rolling movement on said convex surface toward saidcore when said coil is energized, biasing means acting on said armatureto move said armature away from said core when said coil is deenergized,said convex surface being related to said core and biasing means so thatthe contact between said armature and said convex surface moves nearersaid core and away from said biasing means acting on said armature assaid armature moves toward said core, and means for supporting saidarmature on said frame topermitjsaid armature to roll freely on saidconvex surface toward and away from said core, said means including noother contact between said armature and said frame except said contactbetween said armature and said convexsurface which moves nearer saidcore andaway from said biasing means acting on said armature as saidarmature moves toward said core. 7

2. An electromagnetic deviee according to claim 1 in which saidsupporting means includes a pair of links pivotally connected betweensaid armature and said frame; 3.fAn electromagnetic device according toclaim 2 in which said links are'of non-magnetic material and arepivotally connected to said armature by means of a pin fastened alongone-edge of said armature.

4. In an electromagnetic device, a magnet frame having a core, anenergizing coil mounted on said core; an

I armature mounted for swinging movement toward said core when said coilisenergized, biasing means acting a on said armature for moving saidarmature away from said core whensaid coil is deenergized, means forreducing the length of the moment arm with which the magnetic force actson said armature and for increasing the length of the moment arm withwhich the biasing force actson saidarmature as said armature movestoward saidcore, and means'including a pair of links pivotallyconnectedbetween said armature and said frame for supporting said armature'onsaid frame to' permit said armature to swing freely toward said core,when said coil is energ zed. i I

a References Cited in the file of this patent UNITED STATES PATENTS, I

1,714,336 Yaxley May'21', 19 29 2,120,178. Hausrath June 7, 1938 i iFOREIGN PATENTS I l 695,555 Germany Aug; 28, 1940' 822,407

Germany Nov. 26,1951

than

